How to Install Android M 6.0 in Samsung Galaxy S3 I9300

This is the short,easy and secure guide on how to upgrade Samsung Galxy S3 to Android 6.0 Marshmallow or on How to install Android M 6.0 in Samsung Galaxy S3 I9300

After the launch of Samsung Galaxy S3 it didn’t got any further support from the official developers but meanwhile it got an awesome support from awesome developers which results that it got the cyanogenmod 13.0 or cm13 custom rom for samsung galaxy s3. A developer from xda made custom rom android marshmallow 6.0 for samsung galaxy s3.